Method of forming fissured acoustical panel



May 19, 1970 G. E. SAUER ETAL v3,513,009

METHOD OF FORMING FISSURED ACOUSTIGAL PANEL Filed Dec. 27, 1965INVENTORS Arthur C. Austin Gale E.Souer 77, ATTORNEY United StatesPatent US. Cl. 117-10 6 Claims ABSTRACT OF THE DISCLOSURE A buildingpanel is formed by combining a face layer of a relatively low densitymineral fiber and binder composition with a relatively dense gypsumboard back layer.

The present invention relates to a method of forming an improvedacoustical panel. More particularly, it relates to a method of forming afissured acoustical panel adapted for mechanical suspension as soundabsorbing and attenuation media spaced below a main ceiling structure.

The formation of acoustical products, such as tiles and panels, requiresa balance between physical properties. Sound absorption is a criticalrequirement and depends upon the porosity of the material, so thatincident sound waves impinging on the material can enter into thematerial and be dissipated therein. In order to increase the porosity ofthe acoustical product, the surface of the body is usually opened, as byforming fissures or drilling holes therein, to expose the fibrousstructure in the interior of the product, thereby greatly increasing thesound absorbing efficiency of the product. Therefore, as the porosity ofthe body increases and the density decreases, sound absorptionincreases. However, as the porosity increases, the strength of theproduct decreases; and as the density decreases, sound transmisionincreases. Since prefabricated acoustical tiles and panels must reducethe transmission of sound and serve as a ceiling as well as absorbingsound, the material must have sufficient strength to withstand handlingand to be applied on mechanical suspension systems. In addition, thematerial must have sufiicient density so that unabsorbed sound is nottransmitted through the material into adjoining areas. This is ofparticular importance when the acoustical material is installed on amechanical suspension system where the chamber above the suspendedceiling acts as a duct to spread unabsorbed sound waves transmittedthrough the acoustical material into areas where the sound waves areobjectionable. Furthermore, the acoustical material must have anattractive surface so that the ceiling formed will not be aestheticallyobjectionable.

One of the chief disadvantages of presently available porous acousticalbodies, such as those formed of mineral wool, wood fibers, and the like,is that acoustical panels formed of such materials have a tendency tosag excessively when mounted in mechanical suspension systems, such asexposed grid systems. This is especially true when the panels areexposed to conditions of high humidity. Conventional porous, low densityacoustical panels also generally lack sufiicient density to prevent thecontinued upward movement of sound waves traveling through the materialso that an objectionable amount of sound passes through the panel. Whileit has been suggested to increase the density of the product to therebyincrease the sound attenuation, such an increase in density considerablyreduces the sound absorption, which is the principal function of theproduct.

It is therefore an object of the present invention to provide anacoustical panel having the combined properties of high soundabsorption, high sound attenuation, and ade- 3,513,009 Patented May 19,1970 quate strength for mounting in a mechanical suspension system.

Another object of the persent invention is to provide an acousticalpanel adapted for mechanical suspension and which adequately preventsthe transmission of sound waves while retaining excellent properties ofsound absorption.

Another object is to provide laminated acoustical panels having asound-absorbing facing layer bonded to a soundattenuating backing layer.

A further object of the invention is to provide a method of formingfissures in a sound-absorbing facing layer disposed on asound-attenuating backing layer.

A further object is to provide a screed bar for opening fissures in thesurface of a porous, sound-absorbing material.

Various other objects and advantages will appear from the followingdescription of the invention, and the novel features will beparticularly pointed out hereinafter in the appended claims.

In the drawing:

FIG. 1 is a perspective view of the improved acoustical panel of thepresent invention.

FIG. 2 is a fragmentary cross-sectional view taken along the line 22 ofFIG. 1.

FIG. 3 is a fragmentary cross-sectional view of another embodiment ofthe present invention.

FIG. 4 is a sectional view of the oscillating screed bar of the presentinvention.

According to the present invention, the properties of high soundabsorption, high sound attenuation, and sufficient strength to permitmounting panels in a mechanical suspension system without objectionablesag are combined in a single acoustical product by providing a laminatedpanel having a surface layer of a material which has excellentsound-absorption properties, bonded to a relatively dense backing layerwhich serves to prevent the transmission of sound through the panel andhas sufficient strength so that the panel may be mounted in an exposedgrid system without an objectionable amount of sag. In the embodimentshown in the drawing, the acoustical panel 10 includes a sound-absorbentsurface layer 11 of bonded mineral fibers bonded to a backing layer 12of gypsum board, the gypsum board being constructed of a set gypsum core13 enclosed in paper cover sheets 14. Fissures 15, of irregular shapeand size, are formed in the surface layer, the fissures extending fromthe surface of the layer 12 into the interior thereof to expose thefibrous structure in the interior of the surface layer, therebyincreasing the sound-absorption capacity of the panel. In addition, thefissures are also decorative in that they provide a surface resemblingnatural travertine stone.

More particularly, the surface layer 11 consist of granulated mineralwool in a starch binder which is cast on the backing layer. Since themineral wool surface layer is cast rather than being felted, it ishighly capable of giving a natural fissured structure when subjected toa screeding operation. The surface layer 11 provides the acousticalpanel with sound-absorption properties and is relatively uniform inthickness, having a thickness sufficient to permit the requiredpenetration of the fissures produced by the screeding operation. Thethickness of this surface layer directly affects the sound-absorptionvalues of the acoustical panel, for the noise reduction coefficient ofacoustical panels of this invention increases as the thickness of thesurface layer increases. Generally, the surface layer may have athickness in the range of about 7 inch to V2 inch or more. However, itis preferred that the surface layer be no more than about /2 inch thick,for the use of a thicker layer requires extended drying periods andincreases the cost of the product. Preferably, the surface layer has athickness of about inch to inch, for acoustical panels having a surfacelayer of such thickness have excellent sound-absorption properties, arerelatively inexpensive, have good sag resistance, and may be driedwithin short periods of time.

As noted hereinabove, this surface layer preferably consists ofgranulated mineral wool in a starch binder,

the surface layer preferably having a composition, by weight on a drybasis, within the range set forth in Table I.

In such surface layer compositions, the starch and mineral woolcomponents provide the body of the layer. The boric acid functions as aflame inhibitor and a fungicide. The clay provides body, fire resistanceand high temperature dimensional stability. The mineral wool used informing the surface layer preferably has a size such that essentiallynone of the wool is retained on a A-inch screen and from to is retainedon a /z-inch screen, the mineral wool fibers having a diameter of about3 to microns. Conventional thickeners, such as, for example,hydroxypropylmethyl cellulose, ethyleneoxide polymers, guar gumderivatives, and the like, are used in forming the surface layer. Inaddition to the components listed above, the surface layer may, ifdesired, also contain about 3% to 4% stucco to increase the whiteness ofthe layer and about 1.4% to 1.5% of a wax emulsion which acts as asizing to prevent water penetration.

The backing layer 12 is formed of a conventional gypsum board containinga set gypsum core 13, providing structural solidarity and density, andpaper cover sheets 14, enveloping the gypsum core and providing tensileand fiexural strength. This backing layer may have a thickness ofbetween about A inch and inch, with thicknesses of about -"/s inch and/2 inch being preferred. The backing layer provides the acoustical panelwith sufficient strength to resist sagging when mounted in exposed gridsystems and suflicient density to reduce sound transmission so that thepanel has a good sound attenuation rating.

Instead of using conventional glysum board, which has cream-faced paperas the upper covering sheet, it has been found to be advantageous to useas the backing layer a gypsum board in which the top plies of the papercover sheet are unsized. It has been found that the surface layer isbonded more securely to the backing layer when the cover sheets of thebacking layer are unsized. In addition, it has also been found to bedesirable to use as the backing layer, a gypsum board containing nopaper cover sheet on the surface on which the binder-mineral wool layeris deposited, as shown in FIG. 3. It has been found that acousticalpanels produced according to this embodiment of the invention haveoutstanding sag resistance.

In accordance with the present invention, the acoustical panels are madeby forming a wet mix of the ingredients set forth in the table above anddepositing a layer of this wet mix on a previously formed gypsum board.The wet layer is then screeded to provide a surface layer of relativelyuniform thickness, and to open fissures in the wet layer. The slabs arethen dried, whereupon the binder in the surface layer functions as anadhesive to bond the two layers into an integral panel which is then cutto size. As will be described more fully hereinafter, particular caremust be taken in the screeding operation, in order to prevent scrapingthe wet mix off the gypsum board backing layer, and in the drying step,in order to prevent calcination of the gypsum core and/or overdrying ofthe thin surface layer. Usually, the surface layer, as applied, isvslightly greater in thickness than the desired finished thickness sothat the dried material may be planed to a uniform thickness.

In the preparation of the surface layer, the binder, containing all ofthe components listed above in Table I, except the mineral wool, is madeup by dispersing the thickener, such as ethyleneoxide polymers,thoroughly in cold water and subsequently adding the remainder of theingredients in the order listed in the table. Thereafter, thetemperature of the batch is brought up to about 195 F. and maintained atthis temperature for a sufficient time to properly cook the starch,usually not less than about five minutes. Additional water is then addedto provide the binder with a water content of between about and Thebinder and mineral wool are then fed simultaneously and continuouslyinto a twin-screw-type mixer, such as that manufactured by the SproutWaldron Company, in which the mineral wool and binder are thoroughlymixed, the mixture having a deformable but selfsupporting consistency soas to be capable of having fissures formed therein while still in thewet state. Preferably, the mineral wool is mixed with the bindersolution in the ratio of about 3 to 4 parts of binder solution to 1 partof mineral wool. This binder-mineral wool mixture is then cast directlyon the surface of a conventional gypsum board. Preferably, the gypsumboard is carried on a moving conveyor, such as an endless belt, and iscontinuously moved below a container means, holding the wetbinder-mineral wool mix, from which the wet bindermineral wool mix isdeposited on the gypsum board.

The binder-mineral 'wool mixture deposited on the gypsum board backinglayer is then subjected to a wet screeding operation to level the mix,thereby forming a surface layer of a desired thickness, and to openfissures in the surface layer. This screeding operation consists ofmoving the wet mix under a screed bar which extends across and is incontact with the wet mix. As the screed bar oscillates across thesurface of the mix, it levels the mix and opens fissures therein. Whilethis screeding opertion may be performed using only a single screed bar,it is generally preferred to use a pair of spaced oscillating screedbars, the first screed bar leveling the mix to a thickness slightlygreater than the desired thickness of the surface layer, and the secondscreed bar further leveling the wet binder-mineral wool layer to providea surface layer having a uniform desired thickness, the second bar alsoopening fissures in the surface layer as it oscillates thereover. Thefirst screed bar, which first levels the wet deposited mix, ispositioned substantially perpendicular to the surface of the wet mix. Itis mounted so that it extends across the wet mix with the edge of thebar in contact with the wet mix. The second screed bar, which furtherlevels and fissures the surface layer, is positioned at a fixed inclinedangle to the plane in which the mix is moving in order to preventscraping the wet binder-mineral wool surface layer off the gypsum boardbacking layer. Thus, it has been found that if this second screed bar isperpendicular to the surface layer, it scrapes the wet mix off thebacking layer instead of leveling and fissuring the surface layer. This,it is believed, is due to the fact that the binder-mineral wool mix wetsthe paper cover sheet of the gypsum board, causing it to become slipperyso that the wet surface layer is scraped off by the second oscillatingscreed bar. This problem has been overcome, according to the presentinvention, by providing a second oscillating screed bar which is held ata fixed angle of between 15 and 60, and preferably between 30 and 45, tothe surface of the wet mineral wool layer. When the second oscillatingscreed bar is held at such an angle, it appears to exert a slightdownward pressure on the surface layer to somewhat extrude the wet mix,with the result that the wet layer is not scraped off the backing layerbut is leveled to a substantially uniform thickness and fissures areopened in the surface layer. In addition, the use of such an inclinedscreed bar enables the screeding operation to be controlled to producevaried degrees of fissuring.

Such an inclined oscillating screed bar is illustrated in FIG. 4, inwhich numeral 16 indicates the gypsum board backing layer carried onconveyor belt 17 in the direction indicated by the arrow. In theembodiment illustrated in FIG. 4, the Wet binder-mineral wool mixdeposited on the paper cover sheet 18 of the gypsum board has beenscreeded by a first oscillating screed bar (not shown) to form a surfacelayer 19 having a thickness slightly greater than the desired finishedthickness. The second or finish screed bar 20 is positioned at a fixedangle of between about 15 and 60 to the surface layer 19 and extendsacross the wet mix, with the edge of the screed bar in contact with thesurface of the wet layer. In the illustrated embodiment, this secondscreed bar consists of a horizontal bar extending across andsubstantially parallel to the surface of the wet mix, the bar having aninclined edge which is in contact with the wet fibrous mix, with theedge being inclined downwardly in the direction in which the wet mix ismoving, Means (not shown) are provided to support the screed bar andmaintain it in such a position that the edge is held a predetermineddistance above the conveyor belt. Conventional motor means (not shown)are also provided for imparting oscillation to the screed bar in adirection perpendicular to the direction in which the wet mix is moving.This second screed bar removes a slight amount of the surface layer 19to form a surface layer 21 having a uniform desired thickness. Theoscillation of this second screed bar also opens fissures 22 in thesurface layer 21. A curved plate 23 is preferably secured to the backportion of the screed bar to retain the material removed from the layer18 by the screed bar. If the screeding operation is performed with onlya single screed bar, it should be of the type described and illustratedhereinabove; namely, positioned at a fixed inclined angle to the surfaceof the wet mix.

After the surface layer has been cast onto the backing layer andscreeded, the resulting slabs are oven dried to remove moisture from thewet surface layer, whereupon the binder in the surface layer functionsas an adhesive to securely bond the surface layer to the backing layer.The temperature and time of this drying step must be carefullycontrolled in order to prevent calcination of the set gypsum core of thebacking layer and/or overdrying of the surface layer. Calcination of thegypsum reduces the core hardness of the gypsum board, thereby reducingthe sag resistance of the panel. Overdrying of the surface layerdiscolors the surface layer, thereby detracting from the appearance ofthe panel. Therefore, these conditions must be avoided. Generally, it ispreferred to dry the wet laminated slabs at a temperature and timesufiicient to maintain the core hardness of the gypsum board above about20. If the slabs are dried under conditions such that the core hardnessis appreci ably reduced below about 20, the resulting panels will havean objectionable amount of sag when mounted in an exposed grid system.It has been found that drying the wet laminates at temperatures withinthe range of about 250 to 280 F. for up to about four hours will providea panel in which the core hardness of the backing layer is above about20. Slightly higher temperatures, i.e. about 300 F. may be used if thedrying time is correspondingly shortened. Although lower temperatures,i.e. about 180 to 250 F., may, of course, be used, such loweredtemperatures are usually not preferred since their use requires asubstantially longer drying time. After drying, the slabs may be cutinto panels of any desired size. The panels may also be planed, ifdesired, so that the upper surface has a. uniform thickness.

The invention will now be described with reference to a specific examplewhich is intended to be illustrative only. All percentages and parts areexpressed on a Weight basis unless otherwise designated.

EXAMPLE A number of laminated acoustical panels consisting of a poroussound-absorbing surface layer bonded to a sound-attenuating backinglayer were prepared and tested to determined the sound reductioncoefiicient, the sound attenuation value, the core hardness, and the sagresistance of the panels. Each of the panels was made according to theprocedure described hereinabove, the panels having a surface layer ofgranulated mineral wool is a starch binder bonded to a gypsum boardbacking layer. In order to determine the effect of the thickness of thebacking layer, both /z-inch and %-inch gypsum board were used.Similarly, in order to determine the effect of the surface layerthickness, the surface layer on some of the panels was A-inch thick and%-inch thick on other panels prepared in the same manner. Afterfissuring and drying, the panels were tested to determine their noisereduction coeflicient and sound attenuation value, the noise reductioncoefficient being determined by mechanically mounting the panels onmetal supports. The results of these tests are reported below in TableII.

In order to demonstrate the effect of oven drying conditions on the corehardness of the gypsum board backing layer and the relationship of corehardness to the sag resistance of the acoustical panels, a number ofpanels were made according to the procedure described above and driedunder different conditions. The core hardness of each panel and the sagof the panels were then determined. The core hardness value is thenumber of pounds required to force a standard punch, having a 0.093-inchdiameter, /2 inch into the gypsum core. Sag of the panels was determinedwhen the panels were continuously exposed to conditions of F. and 90%relative humidity for controlled periods of time.

Three groups of panels were prepared for testing, all of the panelshaving a Aa-inch thick surface layer having the composition set forthabove and a /2-inch thick gypsum board backing layer. Group A consistedof three sets of panels, one set having a %-inCh surface layer over a/z-inch gypsum board backing layer; a second set having a %-inch surfacelayer over a /z-inch gypsum board backing layer from which the upperpaper cover sheets had been removed; and the third set having a %-inchsurface layer over a /2-inch gypsum board backing layer from the the topplies of paper had been removed. Group B consisted of two sets of panelswhich were the same as sets (1) and (2) in Group A. The panels of GroupA were dried at 230 F. for 2 hours and then at 280 F. for 2% hours. Thepanels of Group B were dried at 280 F. for 5 hours. Group C consisted ofpanels having a %-inch surface layer on a /2-inch backing layer, thesepanels being dried at temperatures between 280 and 430 F. for 13 hours.The core hardness and sag of each of the panels were determined and theresults tabulated in Table III.

The results of these tests clearly indicate that as core hardness of thegypsum board backing layer decreases,

TABLE III Core Sag at 90 F., 90% RH. hard- Panels ness 24 hrs. 48 hrs.72 hrs. 96 hrs.

Grou A:

(1 surface layer, backing layer 24 387 531 585 (2) surface layer,backing layer (paper removed from surface of backing layer) 29 140 149149 (3) surface layer, backing layer (top plies of paper removed frombaeking layer) 19 202 400 520 Group B:

(4) surafce layer, backing layer 523 740 780 (5) surface layer, 56backing layer (paper removed from surface of baeking layer) .455 .630130 Group C:

(6) surface layer 8 1.125 (Mag. on sag rack) Control:

(7) backing layer no surface layer--- 23 313 4.02 .510

the sag of the panels increases, and that the gypsum board should nothave a core hardness much below in order to avoid an objectionableamount of sag in the acoustical panels. Since calcination of the gypsumcore produced by overdrying appreciably lowers the core hardness, itwill be apparent that the drying conditions must be carefullycontrolled.

While the acoustical panels of this invention have been describedhereinabove as having a surface layer of granulated mineral fibers in astarch binder cast on and bonded to a backing layer, it is to beunderstood that other porous, sound-absorbent materials may also be usedas the surface layer. Thus, for example, the surface layer may be formedof felted mineral wool in a starch binder. An acoustical panel may beformed using such a material by laminating a dry sheet of the feltedmaterial to the backing layer with a suitable adhesive, such as thebinder solution. Alternatively, a wet layer of the felted mineral woolmay be pressed on the backing layer and dried, whereupon the binder inthe surface layer will function as an adhesive to bond the layerstogether.

It will be understood that various changes in details, materials, stepsand arrangement of parts which have herein been described andillustrated in order to explain the nature of the invention may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims. Thus, although theinvention has been described in connection with a surface layer of a wetmix of starch and mineral wool, any conventional porous acousticalmaterial capable of being fissured may be used in forming the surfacelayer.

We claim:

1. A method of forming a liminated fissured acoustical panel having aporous surface layer bonded to a dense backing layer which comprisesmixing granulated mineral wool with a starch binder solution to form aWet, deformable, self-sustaining castable mix, depositing said mix onthe surface of a gypsum board backing layer, leveling and openingfissures in said wet mix by moving the wet mix under at least oneoscillating screed bar which extends across and is in contact with thewet mix and oscillates in the direction of its extent thereacross, saidscreed bar being positioned perpendicular to the surface of the wet mix,thereby forming a fissured Wet laminated panel, and drying said wetlaminated panel at a temperature and time sufiieient to maintain thecore hardness of the gypsum board backing layer above about 20 poundsrequirement to force a .093 inch diameter punch to a /2 inch depth,whereby the binder in the surface layer securely bonds the surface layerto the backing layer.

2. The method as defined in claim 1 in which said deposited wet mix isleveled and has fissures formed therein by contacting said wet mix withsaid one and at least one additional oscillating screed bar means, saidscreed bar means being mounted and adapted to oscillate in the directionof their extent across said wet mix, said first screed bar means beingperpendicular to the surface of the backing layer and leveling said wetmix to form a Wet layer having a thickness slightly greater than thedesired finished thickness of the surface layer, said one additionalscreed bar means being positioned on and oscillating across the surfaceof said wet layer to level said mix to a uniform desired thickness andbeing positioned at a fixed inclined angle to the surface of saidsurface layer.

3. The method as defined in claim 2 in which said gypsum board backinglayer is carried on a moving conveyor and is continuously moved below acontainer means holding the wet binder-mineral wool mix, saidbindermineral wool mix being deposited on the surface of said gypsumboard in sufficient amounts to provide, after screeding, a fissuredsurface layer of from about inch to /2 inch in thickness.

4. The method as defined in claim 2 in which said second screed bar ispositioned at a fixed angle of between about 30 and 45 to the surface ofsaid wet layer, said second screen bar being mounted so that the edgethereof extends across and is in contact with said wet layer andoscillates in a direction perpendicular to the direction in which thewet layer is moving, whereby the oscillation of said second screed baracross said wet layer further levels said layer and opens fissurestherein.

5. The method as defined in claim 2, wherein said wet mix comprises, byweight, about 75% binder solution and about 25% mineral Wool, saidbinder solution comprises about by weight water and about 10% solids andsaid binder solution solids comprises about 30% to 60% starch, about 40%to 70% clay and a minor amount of boric acid, said wet mix being leveledto form a surface layer of a thickness of about 7 inch to /2, and saiddrying of said wet laminated panel being at temperatures of from aboutto 300 F. for time periods of about four hours.

6. The method as defined in claim 2 in which said wet laminated panel isdried, said drying being at tempera tures below about 280 F. and beingcompleted in less than about 4 hours.

References Cited UNITED STATES PATENTS 1,983,180 12/1934 McCarthy118-120 2,910,040 10/ 1959 Agahd.

3,391,013 7/1968 Videen 117-10 1,587,699 6/1926 Daniels 162-1162,340,535 2/1944 Jenkins 52-144 X 2,717,538 9/1955 Alexander 162-1162,747,470 5/1956 Jones 162-116 3,061,056 10/1962 Kodaras 52-1453,077,945 2/ 1963 Thomas et al 117-8 X 3,149,005 9/1964 Brundige 118-120X DAVID KLEIN, Primary Examiner US. Cl. X.R.

Patent No. 3! 009 Dated May 19, 1970 Inventor(s) Gale E. Sauer andArthur C. Austin It is certified .that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 4, line 41, "opertion" should be 0peration--.

Column 6, line 8, "determined" should be ---determine---;

same column, line 13, "is" should be in--' same column, line 71, "430should be ---340---.

TABLE III, under the heading 48 Hours in the last line,

"4.02" should be --.402--.

Claim 1, line 1, "liminated" should be ---laminated--.-.

Claim 5, line 8, after "1/2" insert ---inch---.

SIGNED AND SEALED szPmgm (SEAL) Attest:

Auesfing Officer mm 1:. sum. as.

Comissioner of Patents

